1. Field of the Invention
The present invention generally relates to valve driving arrangements for outboard motors. More specifically, the present invention relates to an improved drive pulley mounting arrangement for such valve driving arrangements.
2. Related Art
Outboard motors are used to power watercraft through the water. The outboard motors are mounted to the transom or rear portion of the watercraft and provide a forward or reverse thrust. Because the outboard motor extends upward above a portion of the watercraft, the outboard motor is exposed to passing air streams caused by movement of the watercraft through water. Accordingly, the outboard motor can be a source of wind resistance or drag during movement through the water. This wind resistance results in decreased watercraft speeds or increased loading on the outboard motor.
Accordingly, it is desired to decrease the size of the exposed portion of the outboard motor. In some configurations, the outboard motor is decreased in a lateral direction while in other arrangements the outboard motor is decreased in a vertical direction. By designing a more compact engine that is housed within the outboard motor, the overall dimensions of the outer cowling can be decreased.
It has recently been determined that a mounting arrangement for a drive pulley of a cam drive arrangement could be improved. In particular, the drive pulley typically is mounted to a crankshaft of the engine using a nut that is threaded down over a portion of the crankshaft to engage a top of the drive pulley. This nut is threaded over a portion of the crankshaft having a large outside diameter. This large outside diameter is necessitated by the size of the crankshaft necessary to tolerate the loadings experienced by the crankshaft. The nut size is determined, at least in part, by the diameter of the member to which it is threaded. Accordingly, the nut can only be reduced in thickness to a certain degree. In addition, reducing the thickness of the nut decreases the number of threads that grip the corresponding threads on the crankshaft. Thus, the reduced nut size results in increased opportunity for loosening. Of course, this is a less than desirable solution to the problem of overall height of the engine and its associated components.
Accordingly, an improved mounting arrangement for the drive pulley is desired. Preferably, the mounting arrangement should positively fix the pulley to the crankshaft for rotation with the crankshaft. Moreover, the mounting arrangement should decrease the overall height of the engine and the associated components with the pulley mounted in place.
Accordingly, one aspect of the present invention involves an engine for an outboard motor. The engine comprises an engine case and a crankshaft extending through the case in a generally vertical direction. The crankshaft projects upwardly from the engine case and has a rotational axis. A drive pulley is mounted on the crankshaft and a flexible transmitter connects a driven pulley to the drive pulley. The driven pulley is mounted to a cam shaft and at least one fastener, which has center axis that extends generally parallel to the rotational axis of the crankshaft, joins the crankshaft and the drive pulley.
Another aspect of the present invention involves an engine comprising a generally vertically extending crankshaft. The crankshaft is journalled for rotation within an engine case. A bearing supports an upper end of the crankshaft within the engine case. The crankshaft has a first diameter and a second diameter. A face surface is defined at a transition between the first diameter and the second diameter. A drive pulley is mounted to the crankshaft with at least two fasteners. The face surface is disposed vertically above the bearing.